1. Field of the Invention
The present invention relates to a keyboard apparatus of an electronic musical instrument designed such that the touch response is controlled by way of software.
2. Description of the Related Art
In a conventional keyboard apparatus of an electronic musical instrument, as described in Japanese Patent Laid-Open Publication No. H09-6329, for example, each key is provided with its corresponding mass element referred to as a “hammer” so that a force corresponding to the movement of the mass element brought by a key-depression is yielded as the reaction to the force exerted at the key-depression. As a result, the conventional keyboard apparatus achieves desired touch response having weight which is close to the touch response of the key-depressions of an acoustic musical instrument.
FIG. 1 shows weight characteristics of respective keys of a case in which the touch response of key-depression is mechanically controlled as described above. In order to achieve gradual changes in touch response over all the keys as shown in the characteristics of an acoustic piano indicated by curve “A”, the touch response can be mechanically controlled by providing each of the keys composing the keyboard with a hammer (mass element) corresponding to its own touch response or by gradually varying the position of the support of the respective hammers, which requires more space. In either scheme, however, implementation in actual products is difficult due to problems of manufacturability and cost.
Therefore, actual products are designed such that keys of the keyboard are divided into several groups each containing several keys each having a hammer of the same shape and length so that the several keys physically have the same weight. In those products, as a result, the keyboard is provided with several different weights (touch) in the scaling (transverse axis) direction as shown by stepwise heavy line “G”. The mechanism in which the keyboard apparatus of the electronic musical instrument is provided with different weights G1 through G4 in the scaling direction is referred to as “graded hammer” (registered trademark of the applicant). The designed weights G1 through G4 in which keys contained in a group mechanically have the same weight are referred to as “grade”.
In the keyboard mechanism, however, quite a few movable parts are complicatedly correlated to operate. In addition to tolerances of parts, furthermore, the keyboard mechanism also include many slid areas, resulting in deviation of the weight of the keys contained in a grade. As a result, the weight of the respective keys actually perceived by a player as reaction (touch) deviates from the design as shown by stepwise thin line “Ga”. The worst case can exhibit an inversion phenomenon between light hammers and heavy hammers in which, for example, a key included in the low grade (upper register: high notes) G3 designed to have a light hammer in order to provide the player with a light touch actually provides the player with a heavier touch than keys having a heavier hammer included in the higher grade (lower register: low notes) G2.
Because the graded hammer mechanism has a limit to the number of mechanically available hammer types, furthermore, connections between the grades each having a hammer of different weight result in steps. As a result, there is no way but to draw a stepwise line in the scaling direction brought by the weights of the respective keys as shown by the curve “G”. On the acoustic piano, more specifically, the touch of respective keys gradually varies from key to key as shown by curve “A”, which contributes the player to perceive changes of the touch of the keys as smooth. On the electronic musical instrument of the graded hammer type having several different kinds of hammers, on the other hand, boundaries D1 through D3 where grade-transfer takes place between the hammer grades G1 through G4 produce significant steps between the weights as shown by the curve “G”. Some players realize the steps, which results in their decreased quality satisfaction.